My invention relates to a cathode ray oscilloscope (CRO) or a device incorporating a cathode ray tube (CRT) for sensing and plotting various electrical quantities, or electrical analogs of various physical phenomena, for observation or measurement. More specifically my invention deals with improved means in a CRO for the easy adjustment, as well as reconfirmation, of a zero signal level as represented by a bright horizontal line on a CRT screen.
CROs in general have two orthogonal axes, X and Y, for conveying quantitative information. The X or horizontal axis is normally a linear function of time whereas the Y or vertical axis is linear function of the voltage at the signal input terminal of the instrument. According to a known CRO configuration (shown in FIG. 1 of the drawings attached hereto), the input terminal is connected to the CRT via an input selector and a vertical or signal amplifier. A vertical position adjuster is also connected to the vertical amplifier.
For the setting of the zero signal level on the CRT screen preparatory to signal observation or measurement, the user first operates the input selector to ground the signal input of the vertical amplifier. Thereupon the CRT displays a bright horizontal line. The user proceeds to operate the vertical position adjuster to set the bright line on a desired one of the vertical axis graduations on the CRT screen. Then he again actuates the input selector to reconnect the input terminal to the vertical amplifier, thereby making the instrument ready for the display of an input signal.
Thus the prior art construction has required the user to manipulate the two separate control knobs, associated with the input selector and the vertical position adjuster, for zero level adjustment. I will later explain the difficulties involved in the conventional practice of zero level adjustemnt in some more detail.